The world operates currently through continuous depletion of basic utilities such as energy and freshwater, and sees an ever-increasing cost of raw materials. Thus, it has become increasingly important to improve the sustainability and efficiency of processes of fine chemical and pharmaceutical synthesis. One solution, which enables fewer reagents, less waste materials, high throughput, more efficiency, increased safety and reduced environmental impact, is represented by the use of continuous, small-dimension flow reactors. The use of such continuous-flow devices avoids the drawbacks associated to either conventional “batch” synthesis or scale-up when moving from laboratory to market-size production.
Continuous flow micro-/milli-reactors (reactors having working fluid passage cross-sectional dimensions in the micro- to several milli-meter range) have demonstrated the ability to increase process efficiency due to the intensification of heat and mass transfer processes. The effects on the chemical reactions are beneficial, enabling the reactions to be operated in desirable windows of temperature(s) and concentration(s), thus decreasing the generation of by-products. Furthermore, due to the small in-process volume of continuous flow reactors and their higher controllability, relative to batch reactors, the hazards associated with dangerous chemical processes are considerably reduced.
Despite these advantages, scale up to sufficient production rates can be difficult for some reactions due in part to the large quantities desired. Operating many reactors in parallel—and/or many flow paths in parallel in a single reactor—is one solution. Another is to increase the passage size and the resulting throughput per passage. These two approaches may be combined.
When developing a new reaction process for implementation in a flow reactor, it is desirable and often necessary to work at a small scale initially before transferring the reaction developed at small scales to a higher throughput reactor. In the case of a higher throughput reactor with larger passages, partial heat transfer coefficients (and so total heat transfer coefficients related to the heat transfer area) are reduced, on the one hand, and specific heat transfer areas are reduced, on the other. These two factors lead to a significant decrease of the volumetric heat transfer coefficient. As a consequence, during the scale-up from smaller to bigger passages, the heat transfer performance, expressed by the volumetric heat transfer coefficient, is significantly affected and therefore, a chemical process will perform differently, according to scale.
Corning AFR™ flow reactor modules overcome this problem by the use of glass, with relatively low thermal conductivity, as a module material in the two smallest modules of the AFR line, having small passages and flow rates of from only milligrams per minute up to around 200 grams per minute, and silicon carbide, with much higher thermal conductivity, as a module material in the largest modules having large passages and flow rates of up to a few kilograms per minute. The result is that the thermal performance of a small lab-scale reactor is sufficiently similar to the thermal performance of a larger production reactor that many chemical processes, once developed and optimized at lab scales, can be successfully performed in a production reactor without modification. It would be desirable to extend this scale-up capability to an increased range of reactor sizes and materials, and the widest possible range of reactants or process fluids.